A leaky canister purge valve is a common cause of a lean engine condition, as unmetered air is brought into the intake manifold. Indeed, following a lean engine diagnostic with a CPV integrity test may pinpoint the problem, and prevent warranty testing of all potential causes of a lean engine.
A canister purge valve diagnostic typically comprises closing the canister purge valve and canister vent valve while a threshold vacuum exists in the intake manifold. The diagnostic then monitors fuel tank pressure. If a vacuum build is detected at the fuel tank, a leaky canister purge valve diagnostic code is set.
However, while vehicles sold in North America are required to perform on-board evaporative emissions diagnostics, European Union (EU) and Rest of World (ROW) vehicles are not. As such, vehicle manufacturers may omit the fuel tank pressure transducer and/or the canister vent valve to reduce manufacturing costs. Without the CVV and fuel tank pressure sensor, this type of canister purge valve diagnostic is not practical.
The inventors herein have recognized the above issues and have developed systems and methods to at least partially address them. In one example, a method is provided, comprising: during a first condition, opening a fuel tank isolation valve while maintaining a canister purge valve closed; and indicating degradation of the canister purge valve based on an output of a universal exhaust gas oxygen (UEGO) sensor. The UEGO sensor output will indicate whether any fuel vapor vented from the fuel tank reaches intake through the commanded closed canister purge valve. In this way, canister purge valve degradation may be diagnosed in vehicles that do not include a functional fuel tank pressure sensor or canister vent valve.
In another example, a fuel system for a vehicle is provided, comprising: a fuel tank coupled to a fuel vapor canister via a fuel tank isolation valve; an engine intake coupled to the fuel vapor canister via a canister purge valve; an universal exhaust gas oxygen (UEGO) sensor coupled to an engine exhaust; and a controller configured with instructions stored in non-transitory memory, that when executed, cause the controller to: responsive to an engine lean code, open the fuel tank isolation valve while maintaining the canister purge valve closed; and indicate degradation of the canister purge valve based on an output of the UEGO sensor. In this way, lean engine codes may be arbitrated into canister purge valve degradations and other lean engine code causes. This may decrease warranty costs associated with diagnosing the root cause of the lean engine code.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.